7
Shark Skin Sharks also have a very unique skin texture. They don't have the large, prominent scales found in bony fish. Instead they're covered with smaller, tooth-like scales called denticles. These tough, protective denticles are aligned so that they channel water over the shark's body, minimizing drag due to friction.

17
Respiration -Like bony fish, sharks breathe by extracting dissolved oxygen from water. -The water enters the mouth, passes through the gills and is expelled through gill slits behind the head. In bony fish, these slits are covered, but in most sharks you can see them clearly.

18
Respiration -As the water flows through the gill opening, it passes tiny gill filaments. -These filaments are covered with microscopic blood vessel capillaries, which have a lower oxygen content than the water around them. -This imbalance causes oxygen in the water to diffuse into the shark's bloodstream, where it is distributed throughout the body.

19
Question??? Can a shark stop moving and still breathe? Will they die if they stop?

20
Answer: NO Some sharks have gill pumps called SPIRACLES, a set of muscles that suck in water and push it past the gills. This works something like our lungs -- the shark can continuously gather oxygen while it is in a still position. Most sharks also extract oxygen using ram ventilation, passing water over the gills by moving forward. Some highly- active sharks depend on ram ventilation almost entirely, which means they stay in motion most of the time!

24
Hydrodynamics A shark is more like an airplane. It doesn't have a swim bladder, so it uses its forward movement to control vertical position.airplane The tail is like the shark's propeller -- the shark swings it back and forth to move forward. In an airplane, this forward movement pushes air around the wings. In a shark, this forward movement pushes water around the fins. In both cases, this movement of matter creates lift -- the fluid is different, but the principle is exactly the same.

25
Hydrodynamics The Ultimate Guide to Sharks: How Sharks Swim The Ultimate Guide to Sharks: How Sharks Swim

26
Fins & Movement Sharks have two sets of paired fins on the sides of their body, in the same general position as the main wings and horizontal tail wings of a plane. The shark can position these fins at different angles, changing the path of the water moving around them. When the shark tilts a fin up, the water flows so there is greater pressure below the fin than above it. This creates upward lift. When the shark tilts the fin down, there is greater pressure above the fin than below it. This pushes the shark downward.

29
The shark also has one or two vertical dorsal fins on its back and sometimes a vertical anal fin on its underside. These fins work like the vertical stabilizer wing on an airplane. They help the shark keep its balance as it moves through the water and they can be moved from side to side to turn the shark left and right.

35
Smell Continued Another amazing thing about a shark's sense of smell is that it's directional. The twin nasal cavities act something like your two ears: Smell coming from the left of the shark will arrive at the left cavity just before it arrives at the right cavity. In this way, a shark can figure out where a smell is coming from and head in that direction. Can you think of other animals that behave this way? The Ultimate Guide to Sharks: Shark Smell

36
2. Lateral Line Another unique sense organ is the shark's lateral line. The lateral line is basically a set of tubes just under the shark's skin. The two main tubes run on both sides of the body, from the shark's head all the way to its tail. Water flows into these main tubes through pores on the skin's surface. The insides of the main tubes are lined with hair-like protrusions, which are connected to sensory cells. When something comes near the shark, the water running through the lateral line moves back and forth. This stimulates the sensory cells, alerting the shark to any potential prey or predators in the area.

37
Water flows through the lateral line systems. Vibrations in the water stimulate sensory cells in the main tube, alerting the shark to prey and predators.

38
3. Hearing Sharks also have a very acute sense of hearing. Research suggests they can hear low pitch sounds well below the range of human hearing. human hearing Sharks may track sounds over many miles, listening specifically for distress sounds from wounded prey. The Ultimate Guide to Sharks: Shark HearingThe Ultimate Guide to Sharks: Shark Hearing

39
4. Sight The Ultimate Guide to Sharks: Vibrations and Shark Vision Left Diagram: Chicken nictitating Membrane. Right Diagram: The plica semilunaris is the vestigial remnant of a nictitating membrane in humans. The Ultimate Guide to Sharks: Vibrations and Shark Vision

41
Extra Shark Senses 6. Electroreception The ampullae of Lorenzini give the shark electrosense. The ampullae consist of small clusters of electrically sensitive receptor cells positioned under the skin in the shark's head. These cells are connected to pores on the skin's surface via small jelly-filled tubes. Scientists still don't yet understand everything about these ampullary organs, but they do know the sensors let sharks "see" the weak electrical fields generated by living organisms. The range of electrosense seems to be fairly limited -- a few feet in front of the shark's nose-- but this is enough to seek out fish and other prey hiding on the ocean floor.

54
Skates & Rays vs. Sharks Class Chondrichthyes also contains a number of skates and rays. pectoral fins are greatly enlarged to form "wings" that undulate gracefully during swimming, and the tail fin is reduced or absent. Skates and rays differ from sharks in having few scales and being generally adapted for feeding on bottom-dwelling animals such as molluscs and crustaceans. The bodies of skates and rays are flattened dorsoventrally, enabling them to glide slowly over the bottom in search of prey. Their eyes and spiracles (openings for taking in water) are located on top of the head, allowing them to take in water for gill ventilation while being partially buried in sand.

56
Skates vs. Rays Different Orders Reproduction –Rays are viviparous (live bearing) while skates are oviparous (egg laying), releasing their eggs in rectangular cases sometimes called "mermaid´s purses". Tooth Structure –Although skates may have small teeth, those of rays are plate-like and adapted for crushing prey. Morphology –Skates normally have prominent dorsal fins while those of rays are absent or reduced in rays. Although a few electric rays are capable of delivering a powerful electric shock and some sting rays have large, barbed stingers, in general, these docile animals pose no real threat to swimmers and divers.